1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, and more particularly, to an analog circuit device that requires a stable constant-current source.
2. Description of the Related Art
It is a modern trend to fabricate semiconductor integrated circuit devices that operate at ever high speeds while consuming a constant amount of electric power, while efforts have been made to lower the power-source voltage and to decrease the amplitude of the signals. This trend also applies even to the semiconductor integrated circuit devices constituted by MOS (metal oxide semiconductor or, more broadly, metal insulator semiconductor) transistors or to the analog circuit devices constituted by a CMOS (complementary MOS) circuit that requires a stable constant-current source. Therefore, it has been required to provide a semiconductor integrated circuit device that is capable of producing a stable constant current even on a low power-source voltage.
Further, it has been required to provide a level-shifting circuit capable of operating at high speeds to serve as an interface between a modern semiconductor integrated circuit device that work on a low power-source voltage (e.g., 1.8 V, 1.2 V or lower) to produce signals of a small amplitude and a conventional semiconductor integrated circuit device that work on a high power-source voltage (e.g., 3.3 V or 2.5 V) to produce signals of a large amplitude.
The prior art and its associated problem will be described in detail later with reference to relevant drawings.